Private spaceflight projects have attracted many space enthusiasts disappointed with NASA's progress in human spaceflight. Enthusiasts have cast the new generation of space entrepreneurs in a rosy and romantic light, as cutting-edge innovators who could realise the dream of human spaceflight for the world at large ? or at least those rich enough to pay the bill. Rutan's impressive record of achievements, capped by winning the X Prize with SpaceShipOne in 2004, made him a new space hero.

But failures were inevitable. NASA had many of its own in the early days of spaceflight, from fizzled launches to the Apollo 1 fire in 1967 that killed three astronauts. So have private space ventures, but previously they cost only money and equipment, not lives. The Scaled Composites blast happened during what Rutan called a routine test of the system that pumped nitrous oxide, the oxidiser for his second-generation spacecraft called SpaceShipTwo. It's not clear yet what went wrong, but an investigation is under way. Nor is it clear how long it will delay development of the new craft, which Richard Branson's Virgin Galactic plans to use for space tourism.

Like the successful flight of SpaceShipOne, the explosion marks a milestone in private spaceflight. Ironically, it came just days after another milestone that attracted much less attention ? Northrop Grumman's announcement that it would buy the 60% of Scaled Composites that it didn't already own.

Small companies often lead in innovation, but lack resources as well as bureaucracy and corporate overhead. Have the little space companies reached the point where safety officers looking over shoulders will help rather than get in the way? Do they need the deep pockets of big companies to move beyond demonstration flights? Or will corporate bureaucracy always be a dead weight slowing the pace of innovation?